Noroviruses (NIAID category B priority pathogens) are a leading cause of food- or water-borne gastroenteritis outbreaks, responsible for an estimated 23 million cases annually in the US. However, currently there are no commercially available vaccines or antivirals against noroviruses. We have initiated a comprehensive plan aimed at developing anti-noroviral therapeutics in cooperation with medicinal chemists and virologists from various institutes. Using a novel cell-based Norwalk virus (NV) replication system, we have identified viral proteinase (Pro) and cellular acyl-coenzyme Axholesterol acyltransferase (ACAT) as potential therapeutic targets and have furthermore demonstrated that two classes of compounds significantly reduced virus replication, presumably via the inhibition of viral Pro and ACAT, respectively. Since NV Pro and ACAT play a critical role in viral replication, the hypothesis is advanced that agents capable of inhibiting these enzymes selectively are of potential therapeutic value. Thus, the long term goal of this program is the development of novel small molecule therapeutics against human noroviruses by advancing the active compounds through the stage prior to filing an IND application with the FDA. We have established the following specific aims for advancing our hit compounds into a drug candidate for preclinical development. Specific Aim 1: Utilize medicinal/combinatorial chemistry and molecular modeling to optimize two classes of compounds. The goal of this aim is to identify lead compounds that meet potency, selectivity, c log P, bioavailability, and other relevant parameters for drug development. Aim 2. Conduct in vitro studies to establish the mechanism of action of two classes of compounds. We will also evaluate viral resistance to lead compounds by long-term treatment. Aim 3. Conduct ADME/TOX and oral bioavailability studies to optimize the phamacokinetic parameters of selected lead compounds. Aim 4. Demonstrate in vivo efficacy of lead compounds using the gnotobiotic pig model of human norovirus infection. Accomplishment of these specific aims will set the stage for conducting IND-enabling studies, including large-scale GMP synthesis of lead compounds, pharmacokinetics, GLP toxicology and safety pharmacology. RELEVANCE (See instructions): Human noroviruses are now the leading cause of food- or water-borne gastroenteritis illnesses, but currently there are no commercially available vaccines or antivirals against them. Our studies aim at advancing our hit compounds into a drug candidate for preclinical development, which will have a significant impact on norovirus research and public health.